Is 26 AWG good enough for a ~1.5 amps current at 5V?
So far OK for power.

Since each 5V RGB LED has much more onboard Resistors than a short span of light gauge wire, the loss is small until you cascade much more than what you show.  i.e. whatever causes the voltage across bus to drop below 3.5V


Short strips are OK, but not 5 meters.  
You can estimate the loss from each wire Power and ground from AWG tables Ohms/meter * AMps = Volts (x2 for PWr and gnd)
AWG 26 =133.8 Ohms /km or mOhms/m  =   0.134 Ω/m 


0.134 Ω/m * 3A max *2 (pwr+gnd) = 0.8V /m so 1 meter is tolerable dropping 5 to 4.2 but then LEDs use 3.4V multiplex'd * modulated for brightness



WS2812B specs Power supply voltage VDD = +3.5 ~ +5.3 V

So still regulated ok on 1m with 4.2V maybe 2m wire would work but then we get into EMI interference issues with data errors from unknown interference poor grounding.  COM ERRORS.