Just a simple, but tedious edit of 19 Havok Behavior Graph (hkx) files made possible by this guide, the guides referenced in it and the awesome hkxpack.

To summarize the guides:

1. Verify if the animations are too fast.
2. Check if the mod author provided separate animation files for power armor race. If not, make a copy of the regular biped race animation files.
3. Unpack each animation file needs fixing with hkxpack.
4. In the hkobject with a class attribute called "hkaSplineCompressedAnimation", multiply hkparams named "duration" and "time" by 1.5.
5. Repack xml files back to hkx with hkxpack.

If this mod doesn't work, make sure your fallout4custom.ini has the following:
[Archive]
bInvalidateOlderFiles=1
sResourceDataDirsFinal=

I'm considering writing a small script to automate it if I'm gonna do this a lot.

Here is the script I just made since AER15 is a lot more work by hand.