Hi hello it's ya girl. I'm gonna teach you everything you've ever wanted to know about bomb jumping in Metroid Prime and more! (In a likely very sporadic, disorganized, off-the-cuff manner).

Basics:

Bomb timer:
I know this is very very basic, but I want to start from the start here. Laying the first bomb in the set of 3 bombs will start a 3-second timer. When the bomb timer finishes counting down, you will regain all 3 bombs again. When and if the second and third bombs of a set are laid will have no impact on this timer.

Burning a bomb:
Using the first bomb in a set of 3 to start the bomb timer is called "burning a bomb". It allows for you to use 5 subsequent bombs in one jump after, by having the timer finish counting down just after the final bomb in the first set is used.
You burn a bomb, wait, use the 2 bombs remaining to initiate the 5 bomb sequence, timed in such a way that after the 2nd bomb (3rd in that bomb set, second in the actual sequence) is laid, the timer runs out and you have 3 more.
Bomb jump names:
I'm going to draw some diagrams to illustrate the common styles of bomb jump along with their names (as I've personally come to understand them).

Wall Friction and IBJs:

Bomb Jumping for distance:

Rambling:

It's important to know that where the bomb is in relation to Samus has no impact on height. Bombs always give 23.516 vertical velocity. This means hitting the top of a low bomb, or the bottom of high bomb, will give the same overall height if Samus was in the same position in both hypotheticals.

With this, it becomes clear why visuals do not necessarily dictate the height of a bomb jump. A sloppy-looking set up can yield equal results to a clean looking bomb jump. All that matters is that Samus is in the same position when the final bomb goes off. If 2 bombs are laid the same amount of frames apart, but with different distances between them, as long as both are touched, you will gain the same height.

With that, the 1.5 bomb jump is very easy to gasp. Laying 2 bombs 3 frames apart causes you to hit the center of the first bomb, and then very top of the second bomb. Because the range of bombs is not infinite, it is obvious why laying 3 grounded bombs in succession wouldn't actually give extra height compared with laying 2 of them. Samus is going to hit the top of the last grounded bomb either way, be it bomb #2 or bomb #3, Samus will leave that point with 23.516 velocity.

As a side note, in the Wii versions of Prime games, you can mimic the 1.5 bomb jump with spring ball. Spring ball 3 frames before a bomb goes off to touch the top of the grounded bomb rather than the center. This is how the jump for Space Jump Early is done. (In Metroid Prime 3 the bomb radius is much smaller and you only have 1 frame to spring ball if I remember correctly).

Unmorphing:

Optimal unmorphs timing differs depending on whether or not you have Space Jump. With Space Jump, the vertical unmorphed speed-cap is 14.0, and without is 11.66 repeating.
These number are important because unmorphing with greater velocity than your respective speed-cap will set your speed to that cap. Unmorphing with 14 speed would be optimal with Space Jump, but cut your speed down to 11.66 without.

Because bombs always give the same vertical velocity, in a situation without any friction, the optimal-height unmorph timing after hitting the final bomb in a sequence always be:
7 Frames with Space Jump
9 Frames without Space Jump
Well, I should actually add another detail to that. In a situation without any friction, and a jump-state of 2 (falling state).

The "BSJ Timer":

The BSJ timer is the 22 frames after leaving ground while morphed. During this time, your jumpstate has a value of 4. If you unmorph, you will be in a ground-like state. The unmorph animation lasts longer than 22 frames, but being in a ground-like state on the first frame of unmorph will set your vertical velocity to 0. This ties into the previous section on optimal unmorph timing. If you've touched ground in the last 22 frames, you must wait until the BSJ timer is done to unmorph, if you goal is to ascend.

This timer was lazily named the "BSJ timer" by me, since I didn't know what else to call it. BSJ stands for Bomb Space Jump, an outdated name that has sort of grown past it's literal meaning. A more accurate name would be Ball Space Jump.

BSJ's require an instant unmorph. As I noted, the normal unmorph animation lasts longer than 22 frames, but instant unmorphs only take 1 frame to preform. I don't believe anyone fully understands what triggers instant unmorphs, at least not in any detailed way. The explanation "obstruct the camera and unmorph" will suffice here though. After all, this post is about bomb jumping.

Obstructing the camera in a way that gives an instant unmoprh, in that 22 frame window of the BSJ timer, will allow Samus to jump out of the instant unmorph. This means the optimal unmorph timing for a BSJ (for height) after the first bomb is 21 frames. (This is assuming the bomb hit Samus while she was on collision considered 'standable').

I suppose it's worth noting that the earlier you unmorph, the larger the window to press B. Technically speaking, if you instant unmorph the frame after going air-born in morph ball, you can fall for 20 frames and then still be able to jump. There's not really a practical use for this, as it would be faster, generally speaking, to just delay the unmorph.