: so i'm going to have a lot of waste going from 30 to 19 , or can i
: cut them by half and have strips about 14.5 mm wide

No, certainly not. You have a few other options. If it was my timber, I would find some way to use it that didn't waste any.

One option is to rip the 150mm into about 6 strips that are 22mm wide (assuming you lose about 3mm with the saw kerf). The dress them down to 19mm and then rip the 30mm into 5mm or 6mm strips. The problem with that may be that the grain will not be the way you want. (If you aren't sure what I mean by that, do a search on " quarter sawn" and "flat sawn".)

Another option is to rip it down to about 20mm or 21mm and then dress the sawn faces to give you 19mm strips and thin strips about 8mm wide. Those thinner strips are great for places where the forms have a smaller radius bend. Or you can use the thin strips to create patterns like this. The thin ones bend much more easily.

The option you choose might be determined partly by the equipment you have available.