Since it is paper terrain you want to download you can rescale it when printing or copying.
Can be easilly rescaled for example (from an article by Chris Appoldt), if you want to build a 1/48 scale tank for your aircraft diorama but only have 1/35 scale drawings, simply divide the scale you have by the scale that you want: 35 ÷ 48 = .7291666.
Now round up, leaving you with .73 Adjust the decimal placement to 73 (you’re moving the decimal because on the photocopier, 1.0 = 100%, 1.5 = 150%, etc.). Now just set the copier to make copies at 73 percent, and you have your plans in 1/48 scale. To do the reverse and enlarge 1/48 to 1/35: 48 ÷ 35 = 1.37 Now round up, giving you 137% to enlarge the plans by. Two popular armor modeling scales, 1/35 and 1/76, might complicate matters – most copiers will copy no smaller than 50 percent, and you’ll need to reduce further than that. To convert 1/35 scale to 1/76 scale: 35 ÷ 76 = .46 (or 46 percent) Now, since we can’t go lower than 50 percent, determine the square root of .46, which is .68. Set your copier for 68 percent, copy the 1/35 scale plans, then copy those reduced drawings again at 68 percent. These will give you the 46 percent reduction, and your plans are now in 1/76 scale.
So in this case just up the size slightly even by playing it by eye based on doors etc. should give the desired effect. I did used to play 20mm Napoleonic using 15mm buildings and that worked board wise in terms of spacing etc. rather well and did not look too out but skirmish games will need the right size terrain.