Let's start from the goal. Why should a designer know how to draw? To demonstrate the idea and to "develop artistic taste."
Let's discuss each of these goals.
You can show your interior idea not only with a drawing. The most effective way is to build a 3D visualization (on your own or by the hands of a visualizer).
Drawing has 3 big drawbacks compared to visualization:
1. If something has changed in the interior, you need to redraw everything again
2. Image quality is not photorealistic
3. You can make mistakes with the exact dimensions and proportions. And the result in reality will be completely different, as in the picture.
Therefore, you do not need to be able to draw for demonstrating an idea. For 8 years of active practice (500 design projects), I have not drawn an interior even once.
DEVELOP ARTISTIC TASTE
Drawing skills help the designer, but are not a necessity. I wrote about this in more detail in the article "Higher education or courses".
The time spent on mastering drawing is calculated in years. And the influence of this knowledge on success in work is 5-10%. Much more important are the skills of communication, sales, setting technical specifications for contractors and a theoretical base on engineering drawings.
If you have mastered all this and tested yourself on real projects, then you can devote a couple of years to drawing, just for yourself.