367,851 2015-08-01 00:25:40 9647
Knowing the top 5 blocks is not as important as knowing the average. Unfortunately, although the average is currently very high, the fees are still high.
There are top 10 blocks in 2015 and from this, I believe your guess about average transactions is closely to the fact.
https://blockchair.com/bitcoin/blocks?s=transaction_count(desc)&q=time(2015-01-01..2015-12-31)#f=id,transaction_count,time
367,851 2015-08-01 00:25:40 9647
364,807 2015-07-11 04:58:55 6451
364,972 2015-07-12 08:55:59 6144
365,074 2015-07-13 04:01:36 6084
364,837 2015-07-11 10:09:41 5973
365,068 2015-07-13 02:48:29 5946
364,951 2015-07-12 05:44:07 5944
365,077 2015-07-13 04:43:53 5937
365,047 2015-07-12 23:02:14 5866
Check with this chart, the average transactions per block in 2015 is about 1000 or less than 1000.
https://www.blockchain.com/explorer/charts/n-transactions-per-block