You may end up very regretting joining that Tour. It is going to have 70% of the time spent on the round trip coach bus ride, with may be 45 to 90 min MAX for you to wonder around at the site, inclusive everything.
If you are not that interested, or even familiar with the history of the Moorish occupation Southern Spain for centuries, and the eventually the Reconquista that finally drove the Arabs all the way out of Spain and back to Northern Africa, Granada to you is primarily because it is famous, the "MUST SEE" Alhambra which the main significance is because this being the LAST hold up of the Moorish before driven out.
It is NOT about Isramic art. Although the Palace and Castle have all the delicated, intrigue Islamic art factors all over the place. But its significance is the historical value which to you is a complete waste.