Removing entities in EF6 is very slow using RemoveRange

From reading many other posts it looks like I need to use

context.DbSet<Table>.RemoveRange(…);
context.SaveChanges(); 

to efficiently remove multiple entities.

Sadly however, in my scenario, this is still taking far too long. In tests, even removing 5 entities with about 10 fields takes about 1 sec per entity. This is far too slow.

What else can I do to improve performance?

Edit

This is what the method looks like that does the work:

  public void RemoveClassReportGroupings(IEnumerable<(int clientClassId, int classReportGroupingId)> enumerable)
        {
            List<Class_ReportGrouping> removeItems = new List<Class_ReportGrouping>();

            var dict = _context.ClassReportGroupings.Select(i => i).ToDictionary(i=> (i.ClassId, i.GroupingId));

            foreach (var item in enumerable)
            {
                var removeItem = dict[(item.clientClassId ,item.classReportGroupingId)];
                removeItems.Add(removeItem);
            }

            _context.ClassReportGroupings.RemoveRange(removeItems);

        }