Odoo POS loads very fastly or works well if the number of products and customers are reasonable. That is, the loading time of odoo pos is reasonable in the case of small data. So it will have no issues on loading small amount of data. But on the other hand, if there is large amount of data like hundreds of products and much more customers the Odoo Point of sales can slow down and each session could take more than 15 minutes to load first time. So it will be so difficult to users with large amount of data.
In order to solve this issue of slow loading, Odoo has developed a module named as Pos_cache. Also there are many other customized paid modules available in the market for increasing the performance of your odoo. But odoo pos_cache is free and we can solve the performance issue of pos for an extend. Pos cache module enables a cache on products for a lower Point Of Sales loading time. This creates a product cache per Point Of Sales configuration. pos cache drastically lowers the time it takes to load a Point Of Sales session with a lot of products. It will be slow the first time but faster every next time.
For using pos cache, install pos cache module from apps.
If you need to invalidate cache you can click on invalidate cache button on the top of the point of sales.