What logic boards can I install in my 13” early 2015 MacBook Pro

Apple does not work to maintain sizes, shapes, or electrical compatibility between versions. Everything is optimized for exactly that mainboard, and no others.

You can install EXACTLY the version you removed. Attempts at ANY others are not supported, and you are in for a 'Rite of Passage" sort of adventure is you decide to change to something else.

If you think about it, with the mainboard containing the processor, the boot drive, and the RAM, essentially everything is on that one board. If you decide to change it, you are actually mating a different mainboard to you existing metal can -- a complete waste of your time and energy.

Apple does not sell genuine Apple parts unless you are an Authorized Apple Service Provider. Regardless, even if you can access these parts, a newer logic board would not be designed to work with an earlier Mac model.

Actually I just want to somewhat correct @Grants information since you can install any Logic Board made for the MBPro 13" (2015) laptop. Apple does have several variations with different CPU speeds, and 8GB or 16GB or memory configurations. But as @Grant mentions you cannot install any Logic Board from any other model year into the laptop even if the board would appear to physically fit into the case. The boards for the 2016+ models are completely different than any previous model.