Urdu owes a lot of vocabulary from Persian perhaps 50% but the real problem is not in vocabulary but in sentence structure,pronouns and when spoken. Persian and Urdu may sound a word very different in spite of written in the same way and even conveying the same meaning due to different accents of native speakers and a bit difference in the sounds of vowels. Furthermore nowadays Urdu has adopted many words from English in day to day speech and developed many slangs so the influence of Persian vocabulary is reduced a bit in daily conversation but yes in written form there is a lot of persian vocabulary, Even if Authors,poets and writers don't find a suitable word in urdu they independently use persian words to explain their point of view and nobody minds it rather accepts it whole heartedly. All the great writers and poets of Urdu also know the persian and there was a time not long ago in 70,s  where it was considered compulsory for urdu teachers to learn persian as well, though this trend is declining now a days and that's why urdu is losing its eloquence.Highly vocabulized Urdu is incomplete without persian. Yes! but it is very easy for Urdu speakers to learn persian but same can't be true for persian speakers to learn urdu.