We really need to be able to have more fits considering the amount of content there is, and the amount still to come. A way to organize them into tabs or folders would make them much more manageable.

What is the maximum limit on suit fits? I've never hit it, and I think I have 10-15 fits

All the various modules, weapons, Skills and combinations of same invite experimentation. That very experimentation is limited when the current Fit maximum is discovered. Changing Fitments in Battle can cause the loss of the Battle due to the time required to access the Fit menus.

One aspect of the problem is the unstable state of the Game itself. Accessing menus inside Battles, in particular restocking or modifying Fits, can break the game. I have found nothing to indicate that this has been definitively solved and indeed have Squad mates that have some version of the problem every week to date.

Summary:

Game is unstable so the time consuming task of refitting, while in Battle can break Squads or disconnect Mercs.

Maximum Fits limits experimentation when trying new weapons/modules and combinations.

Assuming the game is as stable it is going to get for the near term increasing the number of Fits seems as reasonable solution.