We are going to China, and we choose Turkish Airlines. We are Pakistan nationals (2 guys) and will be on our business trip to Beijing. We have around 19 hours in Istanbul while going to Beijing, China. Please guide us if it is possible to view Istanbul while staying on-time (15 hours). During our transit period in Istanbul, can we visit Istanbul? Do we have to pay any transit visa fee at the airport?
As far as I can tell, if you leave the airport, you will need a visa. I don't know about the current status but I think the visa-on-arrival is slated to disappear very soon and I am not sure if it was ever available to Pakistani nationals. On the other hand, if you have a visa or residence permit from a European country, you could easily get an e-visa in advance:
Pakistan: Official passport holders are exempted from visa for their travels to Turkey up to 90 days. Ordinary passport holders are required to have visa to enter Turkey. Ordinary passport holders with a valid Schengen, OECD member's visa or residence permit may get their one month single entry e-Visas via the website www.evisa.gov.tr.
Turkish Airlines is very active in promoting stopovers in Istanbul and has many offers including a free guided tour and free accommodation that might be of interest to you. You could also do some sightseeing on your own, 15 hours should be enough but the time of the day will make a big difference for the transportation to and from the airport (see earlier questions on this site).