First of all there is no such thing as WordPress Database in this context. You can use WordPress with MySQL/MariaDB. You can use MySQL/MariaDB that wordpress uses to store your data.
The size of your data is not a problem. The performance is not so straightforward to decide. I think MySQL will come close or better in most of the time. Also you will not be able to use any wordpress Database query helper and have to build everything on your own.
If you still think that you can gain performance using SQLite and all the trouble is worth it, you first need to decide whether it’s the right choice at all.
If you need
Network access – for example accessing from another machine;
Any real degree of concurrency – for example, if you think you are likely to want to run several queries at once, or run a workload that has lots of selects and a few updates, and want them to go smoothly etc.
a lot of memory usage, for example, to buffer parts of your 1Tb database in your 32G of memory.
You need to use mysql or some other server-based RDBMS.
For more details check: https://stackoverflow.com/questions/4813890/sqlite-or-mysql-how-to-decide