Web API or other solution?

I am about to make a website showing products from my database.

I want to register every time a user viewes a product on the website, to be able to show "you have just seen" products.

This mean as I see it, that I need a "tracking service" and a "get products service".

I want to be able to reuse the services for different websites (with different database instances)

I know I can make the services as Web APIs, but is worried about it being to slow.

Is my concern justified? What other alternative ways can it be done?