Your offer of 10 tables for 25k is more then enough. If they want 5 more additional tables they should pay for it themself. Want face dont want give money? they will get some of the money via angpow anyway.

Offer is on table not on cash. You will use your angpow you get to cover the hotel tables. You can tell them you do not have 25k in cash to give as dowry. you can tell them you are paying the hotel via credit.

From the 10 tables, your in laws can keep all the angpow they gather from it, which could amount to 10k to 20k. (2.5k per table is too high priced, as most hotel wedding guest will pay 100 to 200 as angpow only, penang rate that is)

If want cash 10k to 15k is suffice.