I explained it in my post, and if you look up TOE's for Japanese square divisions you will see some of them actually were actually 25,000 men so I was being conservative. The forces committed to a campaign are not just infantry battalions, and not just divisions but all the supporting and logistics troops. You mentioned the Italians sending 75,000 men (which is a real number and not a HOI4 number) and claimed the Japanese were only sending half as many. The triangular Italian divisions prior to switching to the binary TOE would have only had 13,000 men each, so 4 of them come to 52,000 and they actually sent 78,000 men, or 50% more than was in the divisions, to Spain and were able to keep a lot of their base and logistics troops in Italy due to the proximity while Japan would not have had that option.
FYI, a 1936 Japanese template should include:
16 infantry battalions (4 regiments each of which was about 33% larger than European regiments)
4-5 artillery battalions (36-48 guns in the artillery regiment plus 16 75mm mountain guns assigned to the infantry regiments)
1 support AT unit (24 AT guns)
1 recon unit
1 engineer unit
Please don't equate the templates in HOI4 as being representative of actual TOE's as they existed. Every template I've seen so far has been lacking components.