breastfeeding questions

My baby used to nurse for about 10-15 mins on each breast every time day and night making a total of 20-30 mins per session. She's now 2 months old and Suddenly this week she has only been nursing for about 5 mins each breast during the day and at night she only nurses from one breast for about 4-5 mins. She's sleeping 4-6 hr stretches at night and she seems satisfied. She's also having 6-8 wet/dirty diapers a day. Is this drastic change normal?