If your astrology software does not recognize aspects in increments of 15, do not despair!
Its simple. Just take the position of the planet/luminary and add 15° … Let’s use the chart of Louis Pasteur as an example.
Pasteur’s Moon at 17GEM55 has been referred to as ‘unaspected’. Let’s see if there are any 15° aspects. Let’s round its figure up to 18° because it is so close. When we add 15° we get 33. Subtract 30 and that is 3° — which shows us that any 15 aspect will show up +/- 3° in any sign. (18 – 15 also = 3).
What lies 1-5°? Sun & Neptune, just short of 5° Capricorn, which is a 165° aspect (dubbed “Quindecile”).
We would use a tighter 1° orb for the 15° aspect, but an orb of 2° is certainly acceptable for obtuse angles (between 90 & 180), and I think also for the 75° & 105° aspects.
Counting in 15° increments from his Moon position, if Pasteur had anything at 1-4° Gemini or Cancer that would be an aspect of 15°.
If there were antyhing at ~18 Cancer or Taurus, of course, that would be a 30/semi-sextile.
3 Leo or Taurus = 45/semi-square.
18 Leo or Aries = 60/sextile.
3 Virgo or Aries = 75° aspect.
18 Virgo or Pisces = 90/square, of course.
3 Libra or Pisces = 105°.
18 Libra or Aquarius = 120/trine.
3 Scorpio or Aquarius = 135/sesquisquare.
18 Scorpio or Capricorn = 150/quincunx.
Now an opposition to the Moon would fall at 18 Sagittarius. Subtract 15 from that and you get 3 Saigittarius. Add 15 and you get 3 Capricorn. A 165/Qd qualifies for a 2° orb, so we look at 1-5°: Sun & Neptune are there, just short of 5°.