The real problem is actually less the exact rate of 25%, but rather that most of the systems only assume one rate. Denmark was the first country to introduce a general VAT in 1967, and whilst the rate has changed (last in 1992 to 25%), the number of rates have not. So lowering the general VAT rate would likely be possible in a 1-3 year time frame (depending on unknown factors), but lowering the general VAT rate would be a significant loss on state finances (thus not interesting to politicians) (and as someone else pointed out, it mostly favours high spenders, which is also politically dicey).

However, introducing a split rate would definitely require a time frame of at least 4 years, and no politician are willing to wait that long for a politician win.