Yes, you can certainly cut corners in this way. However, you will be missing one of the advantages of RNG which is the massive overlap generated by the method. This of course is not to say that you should not cut corners. If you can get away with it, by all means do it.
I will suggest however that you do it in two different ways (either instead of or in addition to).
Take 10 notes (or ten units).
Your way:
1
12
123
1234
1234..10
First alternative: Back to front.
10
9-10
8-9-10
7-8-9-10
1…2-3-4-5-6-7-8-9-10.
This is very powerful. From a logical poiinto of view it should make no difference if you learned ten notes starting at the first note, or starting at the last. But from a psychological point of view the difference I staggering. If you start at the beginning you will be moving from something you know to something you don’t know. This creates an almost unsurmountable block as the section increases in size.
By proceeding back-to-front you will be proceeding from something you don’t know to something you already know. As the passage increase in size this results in an incredibly empowering inner feeling and as a consequence you feel elated and motivated to keep adding notes at the beginning.
Both these approaches have one major drawback: you will end up practising certain notes (or units) far more than the others.
So if the 10 notes (or units) all have the same difficulty, it is advisable to do RNG. It the end notes are the most difficult, then do it back to front. If the first notes are more difficult, do the way you described. Or you can use a third way, in which you add ntoes both directions. Say, for instance that notes 4-5-6 are the most challenging. Start with them and add one note in front and one note at the end:
4-5-6
3-4-5-6-7
2-3-4-5-6-7-8
1-2-3-4-5-6-7-8.
You get the idea.
Another way ( I find it particularly helpful on chord sequences) is to repeat each note 5 times, then 4, then 3 then 2 and finally as written. The main purpose here is to avoid hesitations. As you repeat the notes/chords, you have time to think about the next note and prepare yourself for a smooth transition:
11111- 22222 – 33333 - ….- 99999 – 10 10 10 10 10
1111 – 2222 – 3333 - … - 9999 – 10 10 10 10
111 – 222 – 333 - … - 999 – 10 10 10
11 – 22 – 33 - …- 99 – 10 10
1 – 2 – 3 -… - 9 – 10.
Finally, if you are going to do RNG, 15 notes may be too much. The ideal number is 7, the minimum number is 5 and I would not tackle more than 10 notes.
Best wishes,
Bernhard.