Query optimzation?

SELECT s.ID ScheduleId
		,sh.Id ShiftId
		,sh.ShiftGroupId ShiftGroupId
		,sh.ShiftName
		,sh.Code
		,sh.StartDtTm ShiftStartDate
		,sh.EndDtTm ShiftEndDate
		,COUNT(sje.StudentId) NumberFilled
		,dbo.GetTotalStudentsNeeded(sh.ID) NumberNeeded
		,sh.Note
		,sh.ShiftPublishedStateId
		,(
			SELECT e2.FirstName + ' ' + e2.LastName + '|'
			FROM Students e2
			INNER JOIN dbo.ShiftClassStudents sje2 ON e2.ID = sje2.StudentId
			INNER JOIN ScheduleShiftClasss ssj2 ON sje2.ScheduleShiftClassId = ssj2.ID
			INNER JOIN ScheduleShifts ss2 ON ssj2.ScheduleShiftId = ss2.ID
			WHERE ss2.ShiftId = sh.Id
				AND (
					ssj2.ClassId = @StudentNameClassIdFilter
					OR (
						@StudentNameClassIdFilter IS NULL
						OR @StudentNameClassIdFilter < 1
						)
					)
				AND @IncludeStudentNames = 1
			FOR XML PATH('')
			) AS StudentNames
		,(
			SELECT CAST(e2.ID AS VARCHAR(50)) + SPACE(1)
			FROM Students e2
			INNER JOIN dbo.ShiftClassStudents sje2 ON e2.ID = sje2.StudentId
			INNER JOIN ScheduleShiftClasss ssj2 ON sje2.ScheduleShiftClassId = ssj2.ID
			INNER JOIN ScheduleShifts ss2 ON ssj2.ScheduleShiftId = ss2.ID
			WHERE ss2.ShiftId = sh.Id
				AND (
					ssj2.ClassId = @StudentNameClassIdFilter
					OR (
						@StudentNameClassIdFilter IS NULL
						OR @StudentNameClassIdFilter < 1
						)
					)
				AND @IncludeStudentNames = 1
			FOR XML PATH('')
			) AS StudentIds
	FROM dbo.Schedules s
	INNER JOIN dbo.ScheduleShifts ss ON s.ID = ss.ScheduleId
	INNER JOIN dbo.Shifts sh ON ss.ShiftId = sh.Id
	LEFT OUTER JOIN dbo.ScheduleShiftClasss ssj ON ss.ID = ssj.ScheduleShiftId
	LEFT OUTER JOIN dbo.ShiftClassStudents sje ON ssj.ID = sje.ScheduleShiftClassId
	WHERE sh.StartDtTm <= @EndDate
		AND sh.StartDtTm >= @StartDate
		AND s.ID = @ScheduleID
	GROUP BY s.ID
		,sh.Id
		,sh.ShiftGroupId 
		,sh.ShiftName
		,sh.Code
		,sh.StartDtTm
		,sh.EndDtTm
		,sh.Note
		,sh.ShiftPublishedStateId

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