Many 25kHz monitors can switch to 15kHz if required. You just have to find one that can do it automatically since powering down the monitor to switch games will suck. Since you mentioned Virtua Figher, I have seen them with Hantarex dual 15/25kHz autoswitch monitors. You should check for that with your supplier.
For a long time 25kHz were avoided since MAME only had the old Atari System 1 (Paperboy, 720, etc.) games that needed it. Recently MAME started support for Sega Model 1/2/3, Konami DJ-Main, Sega System 24, etc. These need 25kHz in the arcades and cannot be displayed on standard res. monitors.
You need to figure out what you want to play and if you want your cab to be ready for the time more 25kHz games will start to appear. Keep in mind many still unemulated Midway games require 25kHz monitors...