TImer1 interrupt Setting
Lets analyse your configuration:

T1CON=0x15


Referring to p79 of the datasheet this means


Prescaler=1
Clock=FOSC/4
Sync=Disable  harmless but ignored
Timer=enabled


... as Mike commented, if your FOSC is 4MHz then you're driving the timer with a 1MHz clock.

Your formula could do with some more brackets:


  Count=65536-((Time*(FOSC/4))/Prescaler)


You want to flip the LED every 0.1s but you can't request the timer to count 100000 because it's only 16 bits. Great time to use the prescaler (that's what it's for) but instead you're counting 50000/0.05s and ignoring alternate interrupts. This happens here

    Counter++;
    if(Counter&gt;1) {
        Counter=0;
        LED_RX=!LED_RX;
    }


Note that on the first interrupt counter goes from 0 to 1 then on the second interrupt it goes 1 to 2 (i.e. greater than 1) resets to 0 and flips the LED.

Finally, this line is plain wrong


  3A98(hex)=15000=65536-(time*4XMhz)/4*1


FOSC=4e6, time=0.05s so 65336-((0.05*(4e6/4))/1)=15336=0x3BE8