Hi,
If the same version number is installed in both websites ; you can copy most of HikaShop tables yes.
The users, orders, download (and some other tables based on "users" table) won't work properly if you don't migrate your users between the two websites. For the products, categories and a lot of other elements, it will work.
If you copy the HikaShop config table ; you would need to check your configuration ; some options are more for J1.5 and other more for J3
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.