The short term fix may be to stage your filtration, so that you start with larger than 20u filters and once all your liquid has been filtered at a larger size, re-run your filtration at 20u (assuming that 20u is your final filtration stage). Without more info on the liquid you’re trying to filter I can’t speak exactly to what your stages should be.
I don’t know what your vacuum setup looks like but in my experience, deeper vacuum/more CFM never hurts, and more surface area as @SoStupendous said. Bel-Art makes an 18" benchtop Buchner that isn’t bad if you make some modifications to it (See here: Winterizing smarter, not harder) otherwise Sambo Creeck makes some enormous winterizing trolleys that use up to 32" diameter filter papers, they sell the largest Buchner’s I’ve seen