Hello community, i wanted to ask that is there any place where i can buy large quantity of bitcoins like 15-20 bitcoins and remain anonymous at the same time. any help would be appreciated

why should be anonymous just to buy bitcoin, if you don't have bad intentions to manipulate the market, then buying bitcoin on the market is not a problem. but if there are other things there must be bad intentions here.
you cant blame a person if they want to hide their identity it is just like doing a bounty and you dont want to submit your KYC form, since 15 to 20 bitcoin is huge amount if we convert in any currency then he only wants to hide its identity because of security issue that is the point.