I recently joined to a team at my work that uses "Check-out lock" in TFS.
Check-out lock means that none of the team members can edit a file while it's checked-out in other team member's computer.
This is the first time I use that kind of lock, usually I work on projects without any locks and I notice that my VS(2015) and my team mates is extremely slow, especially when doing actions such as: adding a new file, get latest version(visual studio is not responding for a while) and writing code.
I recently installed Resharper(VS was slow before I installed it) and under it Performance Guide it marked: Source control plug-in in use as a affecting performance.
Is there a way to prove my concern so my TL will accept my opinion and remove this lock type?
When using exclusive checkouts with TFVC each time you start editing a file, Visual Studio will need to make a server roundtrip to check for the lock status of the file on the server and subsequently lock it. If the TFS server is slow or far away this can take a while. It's likely this team has also configured "Get latest on checkout" which will do a couple of extra round trips.
When adding a file to the solution the problem is aggravated, as Visual Studio will need to lock the project file and the file being added. In case of a new form or control this often results in the creation of multiple files.
In 2012 TFS has introduced a new workspace type of TFVC, the local workspace. This type doesn't support exclusive checkout and keeps edit state locally. As such it's much faster, works better when you're not always connected and generally has much better performance (up to a certain size of workspace). This workspace type is the default workspace type for recent versions of TFS.
The perf issues of your colleagues don't seem to be directly related to the TFVC workspace type nor the use of exclusive checkout though. The warning from Resharper is simply that you have any source control integration enabled:
Source Control | Plug-in Selection: select None for the source control plug-in. This will turn off Git or another VCS provider and improve overall performance.
When using TFVC, only actions that cause server interaction will be slowed down due to the additional network roundtrips. Normal work shouldn't be negatively impacted by it. This suggests your colleagues have other issues on his machine or with the solution they're using. It's likely caused by some extension or due to the large project size. Visual Studio 2015 is the first version of Visual Studio that depends on Roslyn for compilation and it has its issues. In Visual Studio 2017 (especially in 15.6 and later) performance issues have been drastically reduced.
Should you want to convince your boss to stop doing exclusive checkouts, I have some other ammo for you:
Your team is likely used to the fact that they never have to merge things as long as they lock everything. It causes different frustrations. Some perf impact is one of them. But not the perf impact you're describing.