I would either expect the slider to be slideable to the far right end value regardless of the TickStep interval by default. OR there should be a property that allows the slider to be dragged to the end ignoring the TickStep when SnapMode property is set to SnapToTicks
Here is the setup:
<VerticalStackLayout Spacing="25"
Padding="30,0"
VerticalOptions="Center">
<telerik:RadSlider Minimum="1" x:Name="slider"
Maximum="15"
TicksPlacement="End"
SnapMode="SnapToTicks"
LabelsPlacement="End"
TickStep="3" />
</VerticalStackLayout>
and the result, I cannot drag the thumb to maximum value which is 15.