smshort…
If you are considering putting 15% and paying mortgage insurance, but you have the ability to put 20% down and avoid mortgage insurance completely, at that point it will be expensive money to not come up with the extra 5%…
The OP willing to walk away and take a credit hit is a different angle.

Others that talk about potential investment returns and lost opportunity value by larger down payments are just gambling.
Other advice posted is the ignorant leading the blind or vice versa.