Shared CPU was somehow faster than Dedicated CPU

There are 2 types of web application that I have.

Type A

• Application Server => 2vCPUs Shared ,Memory 4GB, $20/m
• Database Server =>2vCPUs Dedicated, 8GB RAM, 25GB Disk, $115/m

Type B

• Application Server => 1vCPUs Shared, Memory 2GB , $10/m
• Database Server =>1vCPUs Shared, 1GB RAM, 10GB Disk, $15/m

Both types use Ubuntu, php, MySQL.

As you can see, the type A is higher spec.
First I created the Type B, and created the Type A based on the snapshot of the Type B. I uploaded the same SQL database, and same php source code.

I run a heavy process with the exactly same condition at both types.

I believed that Type A complete the task much faster, but the result was as follows.

Type A : 21 minutes 40 seconds Type B : 12 minutes 25 seconds

is there anyone who can explain me the reason for the result well ?