We need 9 magic 5x5 squares to construct the 15x15 magic square. We take a (pan)magic 5x5 square and we add each time 25 to all numbers, so we get 9 (pan)magic 5x5 squares with all the numbers from 1 up to 225. We use the 3x3 magic square to arrange the 9 panmagic 5x5 squares.
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9x (pan)magic 5x5 square (adding each time 25 to each number)
| 1 | 2 | 3 | ||||||||||||||
| 1 | 19 | 7 | 25 | 13 | 26 | 44 | 32 | 50 | 38 | 51 | 69 | 57 | 75 | 63 | ||
| 10 | 23 | 11 | 4 | 17 | 35 | 48 | 36 | 29 | 42 | 60 | 73 | 61 | 54 | 67 | ||
| 14 | 2 | 20 | 8 | 21 | 39 | 27 | 45 | 33 | 46 | 64 | 52 | 70 | 58 | 71 | ||
| 18 | 6 | 24 | 12 | 5 | 43 | 31 | 49 | 37 | 30 | 68 | 56 | 74 | 62 | 55 | ||
| 22 | 15 | 3 | 16 | 9 | 47 | 40 | 28 | 41 | 34 | 72 | 65 | 53 | 66 | 59 | ||
| 4 | 5 | 6 | ||||||||||||||
| 76 | 94 | 82 | 100 | 88 | 101 | 119 | 107 | 125 | 113 | 126 | 144 | 132 | 150 | 138 | ||
| 85 | 98 | 86 | 79 | 92 | 110 | 123 | 111 | 104 | 117 | 135 | 148 | 136 | 129 | 142 | ||
| 89 | 77 | 95 | 83 | 96 | 114 | 102 | 120 | 108 | 121 | 139 | 127 | 145 | 133 | 146 | ||
| 93 | 81 | 99 | 87 | 80 | 118 | 106 | 124 | 112 | 105 | 143 | 131 | 149 | 137 | 130 | ||
| 97 | 90 | 78 | 91 | 84 | 122 | 115 | 103 | 116 | 109 | 147 | 140 | 128 | 141 | 134 | ||
| 7 | 8 | 9 | ||||||||||||||
| 151 | 169 | 157 | 175 | 163 | 176 | 194 | 182 | 200 | 188 | 201 | 219 | 207 | 225 | 213 | ||
| 160 | 173 | 161 | 154 | 167 | 185 | 198 | 186 | 179 | 192 | 210 | 223 | 211 | 204 | 217 | ||
| 164 | 152 | 170 | 158 | 171 | 189 | 177 | 195 | 183 | 196 | 214 | 202 | 220 | 208 | 221 | ||
| 168 | 156 | 174 | 162 | 155 | 193 | 181 | 199 | 187 | 180 | 218 | 206 | 224 | 212 | 205 | ||
| 172 | 165 | 153 | 166 | 159 | 197 | 190 | 178 | 191 | 184 | 222 | 215 | 203 | 216 | 209 | 
Use the 3x3 magic square to arrange the 5x5 (pan)magic squares
| 2 | 2 | 2 | 2 | 2 | 9 | 9 | 9 | 9 | 9 | 4 | 4 | 4 | 4 | 4 | 
| 2 | 2 | 2 | 2 | 2 | 9 | 9 | 9 | 9 | 9 | 4 | 4 | 4 | 4 | 4 | 
| 2 | 2 | 2 | 2 | 2 | 9 | 9 | 9 | 9 | 9 | 4 | 4 | 4 | 4 | 4 | 
| 2 | 2 | 2 | 2 | 2 | 9 | 9 | 9 | 9 | 9 | 4 | 4 | 4 | 4 | 4 | 
| 2 | 2 | 2 | 2 | 2 | 9 | 9 | 9 | 9 | 9 | 4 | 4 | 4 | 4 | 4 | 
| 7 | 7 | 7 | 7 | 7 | 5 | 5 | 5 | 5 | 5 | 3 | 3 | 3 | 3 | 3 | 
| 7 | 7 | 7 | 7 | 7 | 5 | 5 | 5 | 5 | 5 | 3 | 3 | 3 | 3 | 3 | 
| 7 | 7 | 7 | 7 | 7 | 5 | 5 | 5 | 5 | 5 | 3 | 3 | 3 | 3 | 3 | 
| 7 | 7 | 7 | 7 | 7 | 5 | 5 | 5 | 5 | 5 | 3 | 3 | 3 | 3 | 3 | 
| 7 | 7 | 7 | 7 | 7 | 5 | 5 | 5 | 5 | 5 | 3 | 3 | 3 | 3 | 3 | 
| 6 | 6 | 6 | 6 | 6 | 1 | 1 | 1 | 1 | 1 | 8 | 8 | 8 | 8 | 8 | 
| 6 | 6 | 6 | 6 | 6 | 1 | 1 | 1 | 1 | 1 | 8 | 8 | 8 | 8 | 8 | 
| 6 | 6 | 6 | 6 | 6 | 1 | 1 | 1 | 1 | 1 | 8 | 8 | 8 | 8 | 8 | 
| 6 | 6 | 6 | 6 | 6 | 1 | 1 | 1 | 1 | 1 | 8 | 8 | 8 | 8 | 8 | 
| 6 | 6 | 6 | 6 | 6 | 1 | 1 | 1 | 1 | 1 | 8 | 8 | 8 | 8 | 8 | 
15x15 magic square consisting of 9 (not proportional) 5x5 (pan)magic squares
| 26 | 44 | 32 | 50 | 38 | 201 | 219 | 207 | 225 | 213 | 76 | 94 | 82 | 100 | 88 | 
| 35 | 48 | 36 | 29 | 42 | 210 | 223 | 211 | 204 | 217 | 85 | 98 | 86 | 79 | 92 | 
| 39 | 27 | 45 | 33 | 46 | 214 | 202 | 220 | 208 | 221 | 89 | 77 | 95 | 83 | 96 | 
| 43 | 31 | 49 | 37 | 30 | 218 | 206 | 224 | 212 | 205 | 93 | 81 | 99 | 87 | 80 | 
| 47 | 40 | 28 | 41 | 34 | 222 | 215 | 203 | 216 | 209 | 97 | 90 | 78 | 91 | 84 | 
| 151 | 169 | 157 | 175 | 163 | 101 | 119 | 107 | 125 | 113 | 51 | 69 | 57 | 75 | 63 | 
| 160 | 173 | 161 | 154 | 167 | 110 | 123 | 111 | 104 | 117 | 60 | 73 | 61 | 54 | 67 | 
| 164 | 152 | 170 | 158 | 171 | 114 | 102 | 120 | 108 | 121 | 64 | 52 | 70 | 58 | 71 | 
| 168 | 156 | 174 | 162 | 155 | 118 | 106 | 124 | 112 | 105 | 68 | 56 | 74 | 62 | 55 | 
| 172 | 165 | 153 | 166 | 159 | 122 | 115 | 103 | 116 | 109 | 72 | 65 | 53 | 66 | 59 | 
| 126 | 144 | 132 | 150 | 138 | 1 | 19 | 7 | 25 | 13 | 176 | 194 | 182 | 200 | 188 | 
| 135 | 148 | 136 | 129 | 142 | 10 | 23 | 11 | 4 | 17 | 185 | 198 | 186 | 179 | 192 | 
| 139 | 127 | 145 | 133 | 146 | 14 | 2 | 20 | 8 | 21 | 189 | 177 | 195 | 183 | 196 | 
| 143 | 131 | 149 | 137 | 130 | 18 | 6 | 24 | 12 | 5 | 193 | 181 | 199 | 187 | 180 | 
| 147 | 140 | 128 | 141 | 134 | 22 | 15 | 3 | 16 | 9 | 197 | 190 | 178 | 191 | 184 | 
I have used method composite, simple to construct
9x9, 12x12, 15x15a, 15x15b, 18x18, 20x20, 21x21a, 21x21b, 24x24a, 24x24b, 25x25, 27x27a, 27x27b, 28x28, 30x30a, 30x30b