I started doing this later, but it can get complicated. If they have two freelancers that have passed the interview, and one is asking for contract amendments while the other is not, we can see what would happen.
But in general, if you insist that they add a termination clause of 15 days on your side, they usually do it although only after some insistence and negotiation, which if you have several interviews ongoing and are waiting for other responses might puts us in a precarious position.
I generally do this as a rule of thumb. Every engagement is a partnership between equals. I have the skills they want. They have the capital I want. We exchange on terms that suit us both or we don't at all. It also sets out the stall as to how the relationship will play out. I've been in enough contracts I need to get out of to save my sanity to know that it's not worth compromising on certain points. Everything on equal footing. The clause will always read something like "either party". There is no way they can legitimately argue against that.
