Closest approach is shown in the mock-up, here. M15 is relatively easy to locate by drawing a line from star Theta (θ) to Epsilon (ε) Pegasi, or Enif.
Extending the line by half as much again will bring you right to M15.
The constellation of Pegasus is best known for the large asterism (unoffiical pattern) known as the Great Square of Pegasus.
This can be seen rising in the east as the sky is getting dark.
Theta and Epsilon belong to the triangular pattern of stars found off the square’s bottom right corner.
Theta is the bottom star of the triangle and Epsilon the rightmost star as seen from the UK.
During the morning of the 3rd, the apparent separation between the centres of M15 and the comet will be less than a degree, (1 degree is two full Moon diameters).
The magnitude of the comet is predicted to be +8.8 at this time.
However, comet magnitudes can be misleading and being an extended object (it’ll have a tangible size in the sky rather than being a point source like a star) will mean that its surface brightness will appear lower than you might expect.
A pair of binoculars should reveal the comet as a faint smudge, but a telescope using a low power will probably fare better.