Computer Instruction Format - Calculating the number of Opcodes
Yes, 14 is right.

You have 8 I type codes, so you can have all I opcodes fit into 13 bits only.

That leaves 3 bits to determine if the opcode is I code or not. You can select one of the 8 bit patterns to indicate that the opcode is I code, which leaves 7 bit patterns for the R codes.

Since R code only needs 12 bits, you have one more bit to determine the R code, which doubles the 7 codes above to 14.

In other words, if 4 top bits define 16 codes, two of those must be reserved for I codes and 14 left for R codes.