Need help identifying breed of new puppy

Hi, my name is John and I am new to this board. I'm hoping some of you could help me identify the breed of my new puppy Joey.

Here is some information that may help.

He is 4 and a half months old.
He is 13 pounds.
He was rescued from Puerto Rico.
The vet at the Rescue labeled him as a Chihuahua mix.
The rescue worker that helped us with the adoption said that she believes he is part corgi since he is heavier than a chihuahua would be and has thick arms and big paws.
The rescue worker said that dogs from Peurto Rico tend to be smaller.
People have told me that they see Beagle, Dachshund, Jack Russell, Mini Pinscher, and Shepherd in him as well.

The rescue worker predicted that he will grow to 15-20 pounds.

Any opinions on breed and adult size would be very much appreciated

Thanks,
John