What is 1.5%rdg + 4dgt for 15,23 V?
Why did you round to 0.2 for just one significant digit? Nothing anywhere in the question has only one significant digit. The operand with lowest number of digits in the question is two so why did you round to just one significant digit?

\$ 15.23 \times 0.015 = 0.23\$ rounded to the same number of significant digits as the operand with the lowest number of significant digits (which is the 1.5%)

Then \$\pm4\$ digits on top of that means \$\pm4\$ of the least significant digit of your reading which was 15.23. The least significant digit of that reading is 0.01. You use the digit from the 15.23 and not the 1.5% because the digit error was quantified relative to your reading. It makes more sense if you just think about how your meter must have an finite minimum absolute error. If it was purely percentage error then it would imply the absolute error of your meter becomes infinitesimal as you approach a reading of zero.

Therefore \$ \pm0.23 \pm0.04 = \pm0.27\$