Looks like "16GB RAM or more is recommended" for macOS based systems.
https://helpx.adobe.com/premiere-pro...uirements.html
For the laptop form factor, the 15" model has quad-core CPU options. If Premier Pro is a multi-threaded application, then it will probably benefit from and take advantage of the additional cores.
https://www.apple.com/macbook-pro-13/specs/#mn_p
In theory more RAM will enable Premier Pro to keep more of its processes in RAM where it can be accessed more quickly by CPU, and in turn more CPU cores mean that more work can be done in a given time frame. These two factors - more RAM and CPU cores - may help reduce the strain currently being put on a minimally spec'd system.
If budget allows, then the iMac may be a better option per ability to support more RAM and multi-core CPU options. Since I don't use Premiere Pro, defer to others (could also ask people at Mac Store for their recommendation) who may have more experience with optimal hardware configurations, but if you can meet the minimum recommended RAM requirements and increase the CPU cores, then the 15" laptop may work.