Hello Mike ,
15 feet x 30 feet is 50m2 not 150m2 lol . You will get about 1lb of wheat seed per sq yd or metre , at harvest , dependant on weather , sowing density , ground conditions etc etc .
A good handful of seed per sq yd will do the job , but i have only ever grown winter sown wheat , end of sept in fact .
I grow an old variety of wheat , 'square heads master' . This variety , from the 1850's , grows to about 5-6 feet tall , and needs no fert .
It gives me the 1lb of seed per sq yd , and about the same in straw . Modern varieties grow to about 2 feet or so tall , and with fert , will give more seed per acre .
I grow wheat , oats , barley and rye , in small amounts , to keep up my fresh seed stock .
All the above cereals are more or less sow and forget till harvest time , they are just grasses after all .
Your wheat may head up by harvest time , if you get it in now . Spring sown barley and oats too . Worth having a go anyway .
Good luck .