Much larger sounds more natural, in my opinion.

With some adjectives we use "Adj+er", with others we use "more Adj", but we can't use those together. Mary is prettier than Susan Mary is more beautiful than Susan If you want to make the adjective stronger, use "much" (much prettier, much more beautiful)

much larger,and here is the rule,large- larger-largerst,exciting-more exciting- most exciting.

Much larger